The present invention relates to a method and a device for controlling an internal combustion engine.
A method and a device for controlling an internal combustion engine are described in German Patent No. 195 48 278. There, a method and a device are described for controlling an internal combustion engine, particularly an internal combustion engine that has a common-rail system. At least one pump delivers fuel into an accumulator and the pressure in the accumulator is detected and controlled to predefined setpoint values by a controller. A valve, which connects the accumulator to the fuel tank, is used as pressure-control means; in addition, a controlled high-pressure pump is used as second pressure-control means.
There are also conventional systems in which only one valve is used for regulating the pressure. The disadvantage of this procedure is that very high power losses occur, since the pump is designed so that it always delivers the maximum required fuel quantity, and the excess fuel quantity is discharged via the pressure-control valve. Very high fuel temperatures can occur because of this power loss. The advantage of this procedure is that the actual pressure is adjusted very quickly and precisely.
Systems equipped with only one controllable high-pressure pump for regulating pressure have the disadvantage that very high demands must be made on the quality of the high-pressure pump.
The change-over to low pressure setpoint values is particularly problematic here. Thus, for example, increased noise emissions can occur during the change-over into overrun, since the low pressure in the accumulator necessary for idling or overrun is first reached after a relatively long delay time has elapsed. The advantage of this procedure is the high efficiency and the low fuel temperature associated with it.
An object of the present invention is to improve the pressure regulation when working with a method and a device for controlling an internal combustion engine. In particular, the object is to increase efficiency and improve the quality of the pressure regulation.
Using the method according to the present invention makes it possible to achieve the advantages of both strategies for regulating pressure without having to accept their disadvantages. This is achieved in that a distinction is made between at least one first and one second operating state based on at least the speed and/or a load signal. In the first operating state, at least one first pressure-control means is used for adjusting the pressure. In the second operating state, at least one second pressure-control means is used for adjusting the pressure. It is recognized in the present invention that at least the speed and/or the load of the internal combustion engine define various states in which different pressure-control means are advantageous. Further performance characteristics and signals can be used for defining the operating states, it is also advantageous if additional operating states are defined.
It is advantageous if the second operating state prevails at great loads and/or at great speeds, and the first operating state prevails at small loads and/or at low speeds.
It is advantageous that the first pressure-control means is a valve, which connects the accumulator to a low-pressure region, and the second pressure-control means is a controlled pump, which delivers the fuel into the accumulator.
Because in response to a fault in one pressure-control means, the other pressure-control means takes over the control, the availability of the internal combustion engine can be increased in the event of a defect.